Impact tools of the wrench or rotary type typically include an electric or air powered motor that is linked to a hammer member. At spaced intervals, the hammer member comes into an abrupt engagement with an anvil member that is operatively connected to a workpiece such as a fastener or some other element that is having work done to
A major problem area of the prior art tools of this type is in the method and structure used for engaging the hammer to the anvil. Due to the abruptness of the contact and the high stresses involved in the transfer of energy to make the impact, the engagement structure that temporarily engages the hammer and anvil is prone to a high rate of wear and failure. This problem appears to be inherent in the mechanical coupling between these two components of the tool. While there have been numerous different methods invented for achieving the temporary coupling between the hammer and anvil, excessive wear and premature failure in the coupling elements continue to be problematic.
There have been some prior art tools in which a fluid clutch is employed to intermittently lock the hammer to the anvil. These tools can suffer from a heat buildup in the clutch fluid (usually oil) which causes the fluid and nearby seals to break down or deteriorate. This heating of the oil is normally a result of the manner in which the fluid is allowed to bypass during the impact/impulse portion of the tool's cycle.
Another problem often suffered by prior art impact/impulse wrenches is that when they employ a sensor designed to shut off the tool when a certain torque limit is reached, the sensing mechanism may be overly complicated and/or inaccurate. In the case of tools that employ a fluid clutch, there is the additional problem that the shut-off mechanism (typically a pressure-sensitive relief valve) causes the tool to vary its impact/impulse energy as the tool approaches its shutoff point. This leads to inaccurate or uncertain torquing of the fastener. In addition, the shut-off mechanism can adversely affect the speed of the tool since some of the tool's energy is going into heating of the fluid.